1. Field of the Invention
The invention relates to the transmission and reception of uncompressed video over a wireless link. More specifically, the invention relates to a delay-less and buffer-less transmission and reception of uncompressed HDTV video over a wireless link enabled to overcome transmission and reception errors.
2. Discussion of the Prior Art
In many houses, television and/or video signals are received through cable or satellite links at a set-top box at a fixed point in the house. In many cases, it is desired to place a screen at a point a distance from the set-top box by a few meters. This trend is becoming more common as flat-screen using plasma or liquid crystal display (LCD) televisions are hung on a wall. Connection of the screen to the set-top box through cables is generally undesired for aesthetic reasons and/or installation convenience. Thus, wireless transmission of the video signals from the set-top box to the screen is preferred. Similarly, it may be desired to place a computer, game controller, VCR, DVD, or other video source that generates images to be displayed on a screen a distance from the screen.
Generally, the data are received at the set-top box compressed in accordance, for example, with the motion picture expert group (MPEG) format and are decompressed by the set-top box to a high quality raw video signal. The raw video signal may be in an analog format or a digital format, such as the digital video interface (DVI) format or the high definition multimedia interface (HDMI) format. These digital formats generally have a high definition television (HDTV) data rate of up to about 1.5 Giga bits per second (Gbps).
Wireless short range transmission in the home can be done over the unlicensed bands around 2.4 GHz or around 5 GHz, e.g. in the U.S 5.15-5.85 GHz band. These bands are currently used by wireless local area networks (WLAN) where the 802.11 WiFi standard allows maximal data rates of 11 Mbps (802.11b) or 54 Mbps (for 20 MHz bandwidth and the 802.11g/802.11a standards). Using the emerging Multi-input Multi-Output technology the data rate of the emerging 802.11n standard can increase to around 200 Mbps. Another alternative is to use Ultra Wide Band (UWB), which claims to provide 100-400 Mbps.
Because the available data rate is lower than the 1.5 Gbps needed for uncompressed HDTV video, the video generally must be recompressed for wireless transmission, when desired. Known strong video compression methods, e.g. those having a compression factor of above 1:30 require very complex hardware to implement the compression. This is generally not practical for home applications. These compression methods generally transform the image into a different domain by using, for example, wavelet, discrete cosine transform (DCT), or Fourier transforms, and then perform the compression in that domain. In PCT application IL/2004/000779, Wireless Transmission of High Quality Video, assigned to common assignee and incorporated herein in its entirety by this reference thereto, there is shown a method of transmitting video images. The method includes providing high definition video, compressing the video using an image domain compression method, in which each pixel is coded based on a vicinity of the pixel, and transmitting the compressed video over a fading transmission channel.
In U.S. patent publication 2003/002582 to Obrador there is described a wireless transmission of images which are encoded using joint source channel coding (JSCC). The transmitted images are decomposed into a plurality of sub-bands of different frequencies. Image and corresponding boundary coefficients with a lowest resolution are sent first and then image and boundary coefficients with a higher resolution are transmitted. An exemplary JSCC applies channel encoding techniques to the source coded coefficients, providing more protection to more important, i.e. low frequency, coefficients and less protection to less important, i.e. high frequency, coefficients.
In coarse transmission methods, signals are transmitted in the form of symbols. Each symbol can have one of a predetermined number of possible values. The set of possible values of each symbol is referred to as a constellation and each possible value is referred to as a bin. In two dimensional constellations, the distance between neighboring bins affects the immunity of the symbols to noise. The noise causes reception of the symbol in a bin that may be the intended bin. If, due to the noise, the symbol is closer to a different bin than intended, the symbol may be interpreted incorrectly. See Ramstad, The Marriage of Subband Coding and OFDM Transmission, Norwegian University of Science and Technology (July 2003).
In U.S. patent application serial numbers; 2004/0196920 and 2004/0196404 by Loheit et al. another scheme is proposed for the transmission of HDTV over a wireless link. The discussed scheme transmits and receives an uncompressed HDTV signal over a wireless RF link which includes a clock that provides a clock signal synchronized to the uncompressed HDTV signal. This scheme also includes a data regeneration module connected to the clock, which provides a stream of regenerated data from the uncompressed HDTV signal. A demultiplexer demultiplexes the stream of regenerated data, using the clock signal, into an I data stream and a Q data stream. A modulator connected to the demultiplexer modulates a carrier with the I data stream and the Q data stream. According to Loheit et al. the RF links operate at a variety of frequency bands from 18 GHz up to 110 GHz, hence requiring sophisticated and more expensive transmitters and receivers.
Transmissions of the types described above also require the use of error detection and error correction means to overcome errors resulting from various transmission and reception faults. One well-known means is the use of an error correction code (ECC) that allows for the correction of the data even if the reception was faulty. However, this solution decreases the effective bandwidth of the channel because many more bits must be sent in addition to the actual data bits. This becomes strenuous, especially when HDTV wireless transmission is necessary. Another way of handling such errors is the use of a retransmit protocol where the receiver, upon detecting an error in reception, requests a retransmit of a portion of the data. This also decreases the bandwidth to an extent, as well as requires at least the transmitter to have a significant buffer to enable such retransmission.
In view of a variety of limitations of the prior art it would be advantageous to provide a solution that enables reliable wireless transmission of an HDTV stream while avoiding the need for complex retransmission requirements, allowing for high-quality transmission of graphics and essentially stationary frames, as well as the error correction at the receive end without the need to handle retransmit protocols nor imposing video frame buffers of large memory capacity.